1. Field of the Invention
The invention relates to the areas of microbial genetics and recombinant DNA technology. The invention provides gene sequences, vectors, microorganisms, promoters and regulatory proteins useful for the production of L-lysine. The invention further provides a method to increase the production of L-lysine.
2. Related Art
L-lysine is an important economic product obtained principally by industrial-scale fermentation utilizing the Gram positive Corynebacterium glutamicum, Brevibacterium flavum and Brevibacterium lactofermentum (Kleemann, A., et. al., Amino Acids, in ULLMANN'S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY, vol. A2, pp. 57-97, Weinham VCH-Verlagsgesellschaft (1985)).
The stereospecificity of the amino acids produced by fermentation makes the process advantageous compared with synthetic processes; generally L-form amino acids are produced by the microbial fermentation process. The production of L-lysine and other amino acids through fermentation, utilizing cheap carbon sources such as molasses, glucose, acetic acid and ethanol, is a relatively inexpensive means of production.
Microorganisms employed in microbial processes for amino acid production may be divided into 4 classes: wild-type strain, auxotrophic mutant, regulatory mutant and auxotrophic regulatory mutant (K. Nakayama et al., in NUTRITIONAL IMPROVEMENT OF FOOD AND FEED PROTEINS, M. Friedman, ed., (1978), pp. 649-661).
Several fermentation processes utilizing various strains isolated for auxotrophic or resistance properties are known in the art for the production of L-lysine: U.S. Pat. No. 2,979,439 discloses mutants requiring amino acid supplementation (homoserine, or L-methionine and L-threonine); U.S. Pat. No. 3,700,557 discloses mutants having a nutritional requirement for L-threonine, L-methionine, L-arginine, L-histidine, L-leucine, L-isoleucine, L-phenylalanine, L-cystine, or L-cysteine; U.S. Pat. No. 3,707,441 discloses a mutant having a resistance to an L-lysine analog; U.S. Pat. No. 3,687,810 discloses a mutant having both an ability to produce L-lysine and a resistance to bacitracin, penicillin G or polymyxin; U.S. Pat. No. 3,708,395 discloses mutants having a nutritional requirement for homoserine, L-threonine, L-threonine and L-methionine, L-leucine, L-isoleucine or mixtures thereof and a resistance to L-lysine, L-threonine, L-isoleucine or analogs thereof; U.S. Pat. No. 3,825,472 discloses a mutant having a resistance to an L-lysine analog; U.S. Pat. No. 4,169,763 discloses mutant strains of Corynebacterium that produce L-lysine and are resistant to at least one of aspartic analogs and sulfa drugs; U.S. Pat. No. 5,846,790 discloses a mutant strain able to produce L-glutamic acid and L-lysine in the absence of any biotin action-suppressing agent; and U.S. Pat. No. 5,650,304 discloses a strain belonging to the genus Corynebacterium or Brevibacterium for the production of L-lysine that is resistant to 4-N-(D-alanyl)-2,4-diamino-2,4-dideoxy-L-arabinose-2,4-dideoxy-L-arabinose or a derivative thereof.
A considerable amount is known regarding the biochemical pathway for L-lysine synthesis in Corynebacterium species (recently reviewed by Sahm et al., Ann. N.Y. Acad. Sci. 782: 25-39 (1996)). Entry into the L-lysine pathway begins with L-aspartate (see FIG. 1), which itself is produced by transamination of oxaloacetate. A special feature of C. glutamicum is its ability to convert the L-lysine intermediate piperidine 2,6-dicarboxylate to diaminopimelate by two different routes, i.e. by reactions involving succinylated intermediates or by the single reaction of diaminopimelate dehydrogenase. Overall, carbon flux into the pathway is regulated at two points: first, through feedback inhibition of aspartate kinase by the levels of both L-threonine and L-lysine; and second through the control of the level of dihydrodipicolinate synthase. Therefore, increased production of L-lysine may be obtained in Corynebacterium species by deregulating and increasing the activity of these two enzymes.
More recent developments in the area of L-lysine fermentative production in Corynebacterium species involve the use of molecular biology techniques to augment L-lysine production. The following examples are provided as being exemplary of the art: U.S. Pat. Nos. 4,560,654 and 5,236,831 disclose an L-lysine producing mutant strain obtained by transforming a host Corynebacterium or Brevibacterium species microorganism which is sensitive to S-(2-aminoethyl)-cysteine with a recombinant DNA molecule wherein a DNA fragment conferring both resistance to S-(2-aminoethyl)-cysteine and L-lysine producing ability is inserted into a vector DNA; U.S. Pat. No. 5,766,925 discloses a mutant strain produced by integrating a gene coding for aspartokinase, originating from coryneform bacteria, with desensitized feedback inhibition by L-lysine and L-threonine, into chromosomal DNA of a Corynebacterium species bacterium harboring leaky type homoserine dehydrogenase or a Corynebacterium species deficient in homoserine dehydrogenase gene; increased L-lysine production is obtained by gene amplification by way of a plasmid vector or utilizing a gene replacement strategy. European Patent Applications EP 0 811 682 A2 and EP 0 854 189 A2 both provide for increased production of L-lysine in Corynebacterium species by way of gene amplification based on plasmid copy number.